2Attribute Based Encryption With Privacy Preserving in Clouds

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International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169Volume: 2 Issue: 2 231 236 ______________________________________________________________________________________

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Attribute Based Encryption with Privacy Preserving In Clouds

M. Suriyapriya 1, A. Joicy 2

PG Scholar 1Assistant Professor CSE Department 2

St.Joseph College of EngineeringSriperumbudur, Chennai-602105

[email protected], [email protected]

Abstract Security and privacy are very important issues in cloud computing. In existing system access control in clouds are centralize d innature. The scheme uses a symmetric key approach and does not support authentication. Symmetric key algorithm uses same key for bothencryption and decryption. The authors take a centralized approach where a single key distribution center (KDC) distributes secret keys andattributes to all users. A new decentralized access control scheme for secure data storage in clouds that supports anonymous authentication. Thevalidity of the user who stores the data is also verified. The proposed scheme is resilient to replay attacks. In this scheme using Secure Hashalgorithm for authentication purpose, SHA is the one of several cryptographic hash functions, most often used to verify that a file has beenunaltered. The Paillier crypto system, is a probabilistic asymmetric algorithm for public key cryptography. Pailier algorithm use for Creation ofaccess policy, file accessing and file restoring process.

Keywords Access control, Authentication, Secure hash algorithm, pailler algorithm. __________________________________________________*****_________________________________________________

I. INTRODUCTION

The mainstay of this is to propose a new decentralizedaccess control scheme for secure data storage in clouds that

supports anonymous authentication. The proposed schemeis resilient to replay attacks. A writer whose attributes andkeys have been revoked cannot write back staleinformation. Distributed access control of data stored incloud so that only authorized users with valid attributes canaccess them. Authentication of users who store and modifytheir data on the cloud. The identity of the user is protectedfrom the cloud during authentication. The architecture isdecentralized, meaning that there can be several KDCs forkey management. The access control and authentication are

both collusion resistant, meaning that no two users cancollude and access data or authenticate themselves, if theyare individually not authorized. Revoked users cannotaccess data after they have been revoked. The proposedscheme is resilient to replay attacks. A writer whoseattributes and keys have been revoked cannot write backstale information. The protocol supports multiple read andwrites on the data stored in the cloud. The costs arecomparable to the existing centralized approaches, and theexpensive operations are mostly done by the cloud.Proposing privacy preserving authenticated access controlscheme. According to our scheme a user can create a fileand store it securely in the cloud. This scheme consists ofuse of the two protocols ABE and ABS. The cloud verifiesthe authenticity of the user without knowing the users

identity before storing data. The scheme also has the addedfeature of access control in which only valid users are ableto decrypt the stored information. The scheme preventsreplay attacks and supports creation, modification, and

reading data stored in the cloud .II. RELATED WORK

ABE was proposed by Sahai and Waters [26]. In ABE,a user has a set of attributes in addition to its unique ID.There are two classes of ABEs. In Key-policy ABE or KP-ABE (Goyal et al. [27]), the sender has an access policy toencrypt data. A writer whose attributes and keys have beenrevoked cannot write back stale information. The receiverreceives attributes and secret keys from the attributeauthority and is able to decrypt information if it has

matching attributes. In Cipher text-policy, CP-ABE ([28],[29]), the receiver has the access policy in the form of atree, with attributes as leaves and monotonic accessstructure with AND, OR and other threshold gates.

All the approaches take a centralized approach andallow only one KDC, which is a single point of failure.Chase [30] proposed a multi-authority ABE, in which thereare several KDC authorities (coordinated by a trustedauthority) which distribute attributes and secret keys tousers. Multi-authority ABE protocol was studied in [31],[32], which required no trusted authority which requiresevery user to have attributes from at all the KDCs.Recently, Lewko and Waters [35] proposed a fully
mailto:[email protected]:[email protected]


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decentralized ABE where users could have zero or moreattributes from each authority and did not require a trustedserver. In all these cases, decryption at users end iscomputation intensive. So, this technique might beinefficient when users access using their mobile devices.To get over this problem, Green et al. [33] proposed tooutsource the decryption task to a proxy server, so that theuser can compute with minimum resources (for example,hand held devices). However, the presence of one proxyand one key distribution center makes it less robust thandecentralized approaches. Both these approaches had noway to authenticate users, anonymously. Yang et al. [34]

presented a modification of [33], authenticate users, whowant to remain anonymous while accessing the cloud.

To ensure anonymous user authentication AttributeBased Signatures were introduced by Maji et al. [23]. Thiswas also a centralized approach. A recent scheme by thesame authors [24] takes a decentralized approach and

provides authentication without disclosing the identity ofthe users. However, as mentioned earlier in the previoussection it is prone to replay attack.

III. PROPOSED WORK

The main contributions of this paper are the following:Distributed access control of data stored in cloud so thatonly authorized users with valid attributes can accessthem.The identity of the user is protected from the cloudduring authentication.The architecture is decentralized, meaning that there can

be several KDCs for key management.The access control and authentication are both collusionresistant, meaning that no two users can collude andaccess data or authenticate themselves, if they areindividually not authorized.Revoked users cannot access data after they have beenrevoked.The proposed scheme is resilient to replay attacks. Awriter whose attributes and keys have been revokedcannot write back stale information.The protocol supports multiple read and write on thedata stored in the cloud.The costs are comparable to the existing centralizedapproaches, and the expensive operations are mostlydone by the cloud .

Fig 1: Secure Cloud storage model

Authentication of users who store and modify their dataon the cloud.The identity of the user is protected from the cloud

during authentication.

The architecture is decentralized, meaning that therecan be seve ral KDCs for key management. There are threeusers, a creator, a reader and writer. Creator Alice receives

a token from the trustee, who is assumed to be honest. Atrustee can be someone like the federal government who

manages social insurance numbers etc. On presenting herid the trustee gives her a token .. For example, these can

be servers in different parts of the world. A creator on presenting the token to one or more KDCs receives keysfor encryption/decryption and signing. In the Fig. 1, SKsare secret keys given for decryption, Kx are keys forsigning. The message MSG is encrypted under the access

policy X. The access policy decides who can access the

data stored in the cloud. The creator decides on a claim policy Y, to prove her authenticity and signs the message


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under this claim. The ciphertext C with signature is c, andis sent to the cloud. The cloud verifies the signature andstores the ciphertext C. When a reader wants to read, thecloud sends C. If the user has attributes matching withaccess policy, it can decrypt and get back originalmessage. Write proceeds in the same way as file creation.By designating the verification process to the cloud, itrelieves the individual users from time consumingverifications. When a reader wants to read some data storedin the cloud, it tries to decrypt it using the secret keys itreceives from the KDCs. If it has enough attributesmatching with the access policy, then it decrypts theinformation stored in the cloud.

A. Creation of KDC

Different number of KDC's are created and to register a

user details. KDC name, KDC id and KDC password aregiven as input to create KDC. Inputs will save in a databaseand to register a user details given a input as username anduser id.

Fig 2: Creation of KDC

B. KDC Authentication

After KDC given a user id to a user, the user willenrolled the personal details to KDC's given a input as username, user id, password etc. The KDC will be verify theuser details and it will insert it in a Database.

\

Fig 3: KDC Authentication

C. Trustee and User Accessibility

Users can get the token from trustee for the file upload.After trustee was issuing a token, trustee can view the logs.User can login with their credentials and request the tokenfrom trustee for the file upload using the user id. After theuser id received by the trustee, trustee will be create tokenusing user id, key and user signature (SHA).

Fig 4: User Accessibility

D. Creation of access policy

After the key was received by the User, the messageMSG is encrypted under the access policies. The access

policies decide who can access the data stored in the cloud.The cipher text C with signature is c, and is sent to thecloud. The cloud verifies the signature and stores the ciphertext C. When a reader wants to read, the cloud sends C. Ifthe user has attributes matching with access policy, it candecrypt and get back original message and user can uploadthe file after user get key from the KDC.

Fig 5: Creation of access policy

E. File accessing

Using their access policies the users can download theirfiles by the help of kdcs to issue the private keys for the

particular users. After trustee token issuance for the users,the users produce the token to the KDC then the tokenverify by the KDC if it is valid then KDC will provide the

public and Private key to the user. After users received the

c c


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keys the files are encrypt with the public keys and set theirAccess policies (privileges).

Fig 6: File accessing

F. File Restoration

Files stored in cloud can be corrupted. So for this issue,using the file recovery technique to recover the corruptedfile successfully and to hide the access policy and the userattributes.

Fig 7: File Restoration

G. Secure Hash Algorithm

Definition: SHA-1 is one of several cryptographic hashfunctions, most often used to verify that a file has beenunaltered. SHA is short for Secure Hash Algorithm.

File verification using SHA-1 is accomplished bycomparing the checksums created after running thealgorithm on the two files you want to compare. SHA-1 isthe second iteration of this cryptographic hash function,replacing the previous SHA-0. An SHA-2 cryptographichash function is also available and SHA-3 is being

developed.

One iteration within the SHA-1 compression function.A, B, C, D and E are 32bit words of the state. F is anonlinear function that varies. n denotes a left bitrotation by n places. n varies for each operation. W t is theexpanded message word of round t. K t is the roundconstant of round t. denotes addition modulo 2 32.

Fig 8: Secure Hash Algorithm

H. Paillier Algorithm

The Paillier cryptosystem, named after and invented byPascal Paillier is a probabilistic asymmetric algorithm for

public key cryptography.

Key generation

Choose two large prime number p and q randomly andindependently of each other such that gcd (pq,(p-1)(q-

1))=1. This property is assured if both primes are ofequivalent length, i.e p,q {0,1 } s-1 for security parameter S. Compute n=pq and =lcm(p-1,q-1).

Select random integer g where gZ* n2. Ensure n divides

the order of g by checking the existence of thefollowing modular multiplicative inverse . = (L(g modn2))-1mod n, where function L is defind as The public(encryption) key is (n,g).. The private (decryption) keyis ( , ).


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Encryption

Let m be a message to be encrypted where m Z n. Selectrandom r where r Z* n. Compute cipher text as: c= g

m .r n mod n 2

Decryption

Cipher text: cZ* n2.Compute message: m =L(c mod n 2).

mod n

IV. CONCULSION

A decentralized access control technique withanonymous authentication, which provides user revocationand prevents replay attacks, is achieved. The cloud doesnot know the identity of the user who stores information,

but only verifies the users credentials. Key distribution isdone in a decentralized way and also hide the attributes andaccess policy of a user. One limitation is that the cloudknows the access policy for each record stored in the cloud.In future, using SQL queries for hide the attributes andaccess policy of a user. Files stored in cloud can becorrupted. So for this issue using the file recoverytechnique to recover the corrupted file successfully and tohide the access policy and the user attributes.

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2Attribute Based Encryption With Privacy Preserving in Clouds